1. Field of the Invention
The present invention relates to a hard material drilling head for a percussion drilling tool, in particular, for a rotary-percussion drill for drilling stone material and having a diameter from 4 mm to 40 mm that is used with a rotary-percussion hand-held power tool. The present invention also relates to a rotary-percussion hand-held power tool equipped with the percussion drilling tool with a hand material drilling head.
2. Description of the Prior Art
Usually, contemporary high-loaded percussion drilling tools for stone materials have a compact solid hard material head with two main and two auxiliary bits and which is mounted on the tool shaft end. In addition to supporting the cutting function of the main bits, the auxiliary bit or bits serve for improving a drilling tool behavior upon hitting the reinforcing metal. Because of a long service life of modern solid hard material head, as uniform as possible drilling capacity of the drilling tool over the period the tool is used, is required. In particular, with new solid hard material heads with still very sharp bits, the sliding friction should not be substantially higher than in a middle of a preset use time period.
International Publication WO 01 088 40 discloses a solid hard material head with three main bits the cutting edges of which are formed of extending from outside inward, a straight outer section and a circular arc section, with the straight outer section being inclined in the radial direction and with the circular arc section extending radially up to the drill tip.
German Publication DE 10 117 262 discloses a compact solid hard material head for a percussion drilling tool having two, diametrically opposite main bits and two diametrically opposite auxiliary bits and in which auxiliary bits, which are arranged, in the rotational direction (at an acute angle) circumferentially in front of the respective main bits, have cutting edges, respectively, extending exactly tangentially.
The tangentially extending cutting edges provide for a reliable lifting of the drilling head, upon the drill striking a reinforcement metal, before the main bits engage the ductile reinforcing metal and can be severely damaged.
European Publication EP 16 047 93 discloses a cross-shaped solid hard material head for a percussion drilling tool with two, arranged diametrically opposite each other, main bits and two, likewise arranged diametrically opposite each other, auxiliary bits which have each an auxiliary cutting edge in form of a circular arc section that is spaced from the rotational axis radially inwardly and extends radially outwardly exacting radially.
An object of the present invention is a solid hard material head having an increased service file.
Another object of the present invention is a solid hard material head having a reduced friction in a new condition.